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214 GREAT BASIN NATURALIST [Volume 55 Wildlife Refuge. This section of the river has the lowest gradient of the entire Green River system. Riparian vegetation consists of willow and tamarix with occasional cottonwoods. We collected monthly samples in the Ouray National Wildlife Refuge (see also Fig. 2). In addition to benthic samples, water chemistry was determined for each habitat type on each sample date (Table 1). Salinity and conductivity were recorded with a YSI meter (Yellowstone Instruments); turbidity was measured with a nephelometer; and hardness, pH, and alkalini- ty were determined with a Hach Kit (Hach Chemical Corporation). Water chemistry was recorded at three locations per sample area on each sample date. At each site, a min-max ther- mometer was placed near the benthos-water interface at the time of sampling and left for 10 days. Substrate composition was estimated visually. River Channel The river channel was sampled approximate- ly 1.3 km north of the United States Fish and Wildlife Service (USFWS) hatchery on the Ouray National Wildlife Refuge. Sampling was adjacent to a sand bar that decreased water turbulence and prevented shifting sands. Water chemistry values were relatively stable. Turbid- ity was substantially higher during the August sample. Substrate consisted mostly of sand with Wyoming Colorado J----I lOOKilometCfS Fig, 1. Regional map showing the location of the Ouray National Wildlife Refuge, little silt and detritus. Water levels were too high during June (peak flow) to allow sampling. Ephemeral Side Channel During high flows the Green River will occupy various smaller channels that are dry during low-flow intervals. We have named such habitats "ephemeral side channels." The ephemeral side channel studied was approxi- mately 2.75 km south of the USFWS hatchery. For most of the year water levels in the main channel were below the level of the ephemeral side channel. However, during peak flow, water filtered through a wooded area and gathered into the channel, which was 10 m wide and 500 m long. As the river level dropped, flow slowed and eventually stopped. Because the side channel dried up shortly after the July sample, no August sample was taken. Most notable of the water chemistry measurements was the increase of salinity and alkalinity when comparing June to July. Water temperature also deviated more during July, Substrate con- sisted mostly of firm silt and detritus with little sand. Sediment deposition contributed little to the site during our study, j Fig, 2, Local map of the Ouray National Wildlife Refuge, Uintah County, UT, showing the location of sam- pling sites, :' - . . .